It was not easy, but the result was worth the many times he almost got lost in Sherlock's subconscious. He almost lost himself, dissolving into meaningless streams in the darkness that surrounded him, but he always pulled himself together before it happened. It was difficult to remember who he was, and what he was doing, he believed, because he was after all only a creation of Sherlock's mind that the consulting detective had no idea would try to turn against him. There had to be an instinct of self-preservation buried deep, otherwise he would not find the idea of simply giving in and letting himself go, become harmless, so appealing. He had not yet detached himself completely from the mind that had created him; he probably never would. It was Sherlock who had given birth to him, to his private enemy, in his very own thoughts; they were linked. It was another reason he had decided to entrap Sherlock rather than try to destroy him. Due to the link, he might be killed off as well if he succeeded. And he had no wish to commit suicide again.

So he concentrated on staying himself amidst the sensations and thoughts that surrounded him while executing his plan.

Slowly, he learned how to control dreams. He didn't know how long it took, and it wasn't important. Time was of no consequence in a person's head. It was a construct that men had first based on sunrise and sunset; it was dark here and would always stay dark. He had never bothered to try and keep track of time since he had woken up in his cell. In life, his other life, he had only paid little attention to the passing of hours, just as much as he needed, so why should he do so now?

He almost missed it when he found it. A thread of the feeling that had told him Sherlock was about to wake up; an unpleasant, unsettling terror, very nearly slipping past him as he tried to make sense of everything he was finding.

He followed it. He knew if he let it out of his grasp, it would be gone forever.

It led him to the dream that had inspired it. At first, he thought it was a memory. It was the day on the rooftop, and he passively watched himself commit suicide through another's eyes.

He only realized it was a dream when a shot rang out and Sherlock ran to the edge of the roof to see John lying on the street, blood flowing from the bullet wound in his head.

Sherlock's subconscious had recognized him as he strolled through the corridors of the mind palace. He smiled as he held unto the dream. It was no longer being dreamt, it was the memory of a dream, to be precise, but if he could change it...

He felt the urge to desist again, but he still tried to bend it to his will, and he succeeded.

Nothing about the rooftop, or himself. It would have been too easy to deduce who was behind it. He gave Sherlock other dreams – the fear of an abandoned child; lying awake at night scared of the dark; an empty field, unknown animals howling in the distance. Fears everyone had felt once in his life. And of course his biggest fear. Failing a case and losing John Watson and his other friends through his mistake.

He had to wait for the right moment to introduce the dream into Sherlock's sleep. He had grown accustomed to distinguish between his waking and sleeping periods; the mind palace felt oddly like a house whose owner was on vacation during the latter. He waited until he needed rest, until he could feel silence descend over the palace, and infused the dream into it by degrees.

He knew he had done well when the subtle terror he had felt while sneaking around reached new peeks. He smiled and felt himself growing stronger. The desire to dissolve lessened considerably. He had found a way in Sherlock's conscious. If he only found one to influence him when awake as well...

But he could be patient and work with dreams for as long as it took. He would never know the period of time that passed outside, but he felt that he had barely begun when the atmosphere changed. He crept out of the darkness and emerged into the mind palace once more to investigate.

It was dark and dreary, fear hiding in the corners. The dreams were doing their work.

He stood still and felt. If he could concentrate these feelings to certain places within the palace, Sherlock would be forced to move, to keep his conscious, or at least a big enough part of it, away. He would not wish to be afraid while working on his cases; it would hamper his investigations immensely.

He suddenly realized that Sherlock hadn't noticed him standing in the middle of a corridor for what might have been a long time. The consulting detective was already too unsettled to keep track of his mind palace.

Dreams and the subconscious. He had always been aware of their power, but seeing it in progress was awe-inspiring. Sherlock had been the master of his mind palace, and he wasn't anymore. All because of dreams.

If he had known what was going on, he would have rejected the possibility haughtily. But he didn't. He had no idea what was about to happen.

He could walk freely around even when Sherlock was awake, as long as he was careful, but it was even more useful to do it, as he had before, when the consulting detective was asleep and he could safely distribute the fear and panic as he saw fit while working on his dreams. He had learned that, as long as he didn't let go, he could split himself for short periods of time. He always returned quickly to the subconscious to merge when he felt weak, though, just to be sure.

It happened more and more rarely that he had to. Sherlock was confused because of the dreams, scared, unsure, and his control was slipping while his grew.

He filled the memory corridors Sherlock was less likely to go first, so he wouldn't realize that the reason of the fear he continually experienced was his greatest enemy alive and well in the one space he had thought safe of him. He decided against trying to fill his subconscious more than it already would through the natural connection. He didn't want Sherlock to go insane and end in a cell in the outside world. Half his fun would be gone then.

He had to be as fast as he could, while at the same time maintaining the same speed throughout. If he stopped or became slower Sherlock would notice. He had advanced far enough that the lack of his influence would be felt just as keenly as his taking over.

He was working his way through the tract that held Sherlock's childhood memories, occasionally being surprised at the harmony and ordinariness of it all – perhaps he should not have judged the consulting detective so harshly, how could he have been extraordinary with such a normal early life? – when something happened. The mind truly had mountains.

Sherlock was working; he could feel the excitement that always stirred him into action. Not even the fear he was spreading could cover it up. In the end, it only served his purpose since Sherlock was even more unlikely to look after a reason for his nightmares.

Later, he decided that the connection between the memory he found himself in – one of Sherlock's first experiments with a chemistry kit – and Sherlock experimenting in the kitchen of his flat – that suddenly transported him.

One minute, he was making his way through a seemingly endless line of Mycroft and Sherlock playing and studying together – how they had come to have such a twisted relationship, he had yet to find out, but he would, he felt certain, no secret was to be kept from him, not anymore – and then he could see.

For the first time since he had woken up chained in his cell, he could see.

He was watching Sherlock's hands filling some sort of liquid into a cup. The shock of finally being able to see the outside again almost made him stay, but then he realized that Sherlock would notice if he lingered, and he returned to the confines of the consulting detective's mind.

That one moment, that one picture, had been exhilarating. And Sherlock hadn't even noticed.

He must be closer to gaining control than he had thought.

It quickly became another one of his goals. See through Sherlock's eyes, each day for a longer period of time.

At first, it was only seconds, but eventually, he stayed for minutes, then hours. As long as he only observed, Sherlock didn't seem to notice.

Neither did John Watson know that their greatest enemy was watching him through his friend's eyes.